1. Field of the Invention
As a result of the pending energy shortage in the United States and other coal-producing countries, current emphasis is on rapid and inexpensive means for distributing the coal to storage and shipping centers, and also to the electric generating plants. A now widely practiced method is pipeline pumping of pulverized coal in aqueous slurry. An existent problem with this practice lies with the efficient recovery from the slurry of both the coal and an environmentally acceptable discharge water. After primary separation of the larger particles, a substantial proportion of the coal remains in the slurry as a colloidal suspension. Attempts to flocculate this residual colloidal coal have relied upon complicated and expensive chemical procedures.
2. Description of the Prior Art
In U.S. Pat. No. 3,717,574, Werneke flocculates coal by a process requiring the combination of pH adjustment to the slightly acid range and the addition of at least two water-soluble anionic polymers or copolymers. One of the polymers must be of low molecular weight and comprise acrylic acid linkages, and the other must be of high molecular weight and comprise vinyl acid linkages. Werneke further teaches that a water-soluble anionic starch acts as an auxiliary flocculant when combined with the low molecular weight polymer in his system. Similarly, in British Pat. No. 1,309,473, Jonason shows starch phosphate as a flocculant for coal washery tailings. While this patent acknowledges the desirability of a truly soluble starch derivative for use as a flocculating agent, the highest starch phosphate solubility obtained therein is 61%. Moreover, this degree of solubility is obtainable only by stringent conditions of preparation.